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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

IRON

163

of extraneous substances (tungsten, chromium, silicon, etc.) may exert a
function analogous to that of carbon.

Of special technical interest are arsenic, phosphorus, sulphur, etc., which
are almost always present in smaU amounts in ferrous products, and should
therefore be determined, both in the crude products to decide methods of
refining, and also in the refined products to ascertain if they are suitable
for the required purpose.

Complete study of these products includes, then, besides exact chemical
analysis, microscopical analysis and mechanical tests (resistance to tension,
shock, crushing, and elasticity and torsion tests, etc.).

The chemical analysis comprises especially determinations of the carbon
(total, graphitic and combined), silicon, manganese, phosphorus, sulphur
and arsenic, the methods employed being described later. In rare cases,
other determinations, such as those of copper, tin, antimony and oxygen,
are required.

In every case, the sampling is of prime importance.

Sampling.—To obtain a representative sample, the whole mass of the
metal should be bored with a small drill free from oil, the greatest cleanli-
ness being observed, and the drillings caught on a sheet of brass or collected
with a magnet. The whole mass should be drilled where possible, as some
products, notably steels, differ appreciably in composition inside and outside.

With large ingots, samples should be taken at the two ends and the
middle, at the surface and interior, and, if it is of no interest to investigate
different points of the mass, a single, homogeneous sample is made of all
the borings.

Small objects of wrought-iron, cast-iron or untempered steel may be
sampled by means of a good steel file, cleaned with ether and benzene, the
object being attacked at different points. Tempered steel must be softened
by heating it in a porcelain crucible unglazed inside placed in a larger crucible
of refractory material.

For very hard products, specially hard steel drills may be used. Failing
this, parts of the object may be broken on an anvil with a heavy hammer
and the small pieces powdered in an agate mortar, the finer material being
sieved away and the coarse repowdered.

1.   Determination of the Carbon

Carbon may occur in ferrous products in four forms :

(a)   Graphitic carbon, consisting of fragments of graphite disseminated
through the mass of the metal and insoluble in acids.

(b)  Annealing carbon, consisting of amorphous graphite, also insoluble
in acids.

(c)   Carbon combined as iron carbide, or carbide carbon, soluble in hot
nitric acid to a brown solution.

(d)  Hardening carbon, contained especially in steel, and also in white
cast-iron, and liberated as gaseous products during the action of hot nitric
acid.

Methods are given below admitting of the determination of the total .......           —